keyboard add ability to specify temporary custom layouts

rb core allows you to load custom keyboard layouts

this patch adds the ability to load a keyboard layout in a buffer
the custom layout is temporary and does not overwrite the current layout

use like so:

    unsigned short kbd[64];
    unsigned short *kbd_p = kbd;
    if (!kbd_create_layout("ABCD1234\n", kbd, sizeof(kbd)))
        kbd_p = NULL;

    rb->kbd_input(buf,sizeof(buf), kbd_p);

Change-Id: I7be2bd4a1b4797a147fa70228a9749dc56ac052a

apps/plugins/lib/kbd_helper.h

@@ -0,0 +1,27 @@
+/***************************************************************************
+ *             __________               __   ___.                  
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___  
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /  
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <   
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \  
+ *                     \/            \/     \/    \/            \/ 
+ * $Id$
+ *
+ * Copyright (C) 2020 William Wilgus
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ****************************************************************************/
+#ifndef KBD_HELPER_H
+#define KBD_HELPER_H
+
+/* create a custom keyboard layout for kbd_input */
+int kbd_create_layout(char *layout, unsigned short *buf, int bufsz);
+
+#endif /* KBD_HELPER_H */